Quantum Chaos Slows Down at Low Densities

In quantum systems with conserved charge, chaos hits a wall as density drops. New research shows that the speed of information scrambling—measured by Lyapunov exponents—vanishes algebraically with charge density. This bound, stronger than any previous limit, is saturated in models like the charged Sachdev-Ye-Kitaev system, revealing a fundamental slowdown in constrained quantum dynamics.

According to the paper, the growth rate of operator size in these systems scales with density, leading to parametrically slower chaos. This has implications for understanding thermalization and black hole analogs in condensed matter.

Reference: Chen, X., Gu, Y., & Lucas, A. (2020). Many-body quantum dynamics slows down at low density. arXiv:2007.10352v3.